Fillers are often added when polyurethane foams are being prepared in order to obtain specific properties in the finished product, to utilize scraps and to reduce the cost of the material.
Conventional fillers include cement, lime, chalk, barium sulfate, fibers, particularly glass fibers, and powder produced from crushed foam scraps.
The operation of working the fillers into the reaction components is known from experience to be accompanied by problems. With smaller proportions of filler, the viscosity is lower. When the viscosity is 40 Pa.s or less and the filler is non-abrasive, gear pumps may be used to introduce the filler into one of the components, preferbly into the polyol. With higher proportions of filler, the viscosity is higher. When the viscosity is 100 Pa.s or less and the filler is abrasive, screw pumps are used. In this case, premixing takes place with one component.
Another apparatus is known in which the filler is supplied packed in an endless tube, the tube being slit directly in front of the inlet of the mixing chamber and carried away into the chamber. The tube itself forms scrap.
The introduction of solid fillers into an agitator mixing chamber via a vibrating feed hopper is also already known.
When metering is being carried out by means of pumps, the disparity between the viscosities of the reaction components and the fillers requires a large amount of energy to effect mixing. Metering by means of pumps is therefore only suitable for continuous operations, since the high viscosity of the reaction component containing filler when compared to the very low viscosity of the other reaction component causes problems in metering the components into the mixing chamber. Furthermore, due to the high viscosity of the component containing filler, the inlet for that component may not close tightly. Faults may result in the finished formed parts when a non-continuous operation, such as filling molds, is used.
Supplying the filler by means of a tube or vibrating channel is particularly suitable for abrasive products. However, considerable problems arise in the exact metering, particularly in non-continuous operation.
The object of this invention is to provide a process and an apparatus with which fillers of any type may be introduced in high proportions by weight and in equal ratio to the other reactants and be homogeneously mixed. Continuous as well as non-continuous operation is possible, and in the case of non-continuous operation it is possible to work with almost no scrap loss.